Abnormal TSH: a rational approach to the older patient.

The clinician whose older patient exhibits an abnormal TSH value must first determine if the result is caused by nonthyroidal illness or a medication whose effect is reversible. Patients without a nonthyroidal cause for the TSH abnormality and corresponding abnormalities in levels of circulating thyroid hormones and/or significant reproducible TSH elevation are usually in need of therapy. Those with normal circulating concentrations of thyroid hormone and potentially reversible signs and symptoms may be considered for a monitored therapeutic trial of treatment. All others need to be followed biochemically regardless of treatment choices. Patients with subclinical thyroid dysfunction require follow-up.